Generally, a tape reel used in a recording tape cartridge such as a video tape cartridge comprises an upper flange and a lower flange with which both top and bottom edges of the recording tape are guided. The inside surfaces of both the top flange and the bottom flange are formed generally flat and the outside surfaces thereof are formed either flat or with radial reinforcing ribs.
However, in the case where such ribs are provided on the flanges of the tape reel, during the molding process, plastic resin materials is injected at a position of the die corresponding to the center of a tape reel and flow into the space for the flange and the ribs. In this case, there may occur a different flow of the plastic resin material for the ribs and the other parts, such as the flat wide flange portion due to a difference of thickness between the ribs and the flat flange portion, so that there may occur defective filling of the plastic resin material or internal strain due to the difference of shrinkage of the plastic resin material during the process of cooling of the casting mold. In the case where the ribs are not formed on the flanges, i.e., the flanges are flat, the flanges have to be made rather thick so as to maintain the mechanical strength of the flanges, thereby producing the disadvantage of lowering the moldability of the tape reels. Furthermore, it is difficult to make the over all surfaces of the flange flat.
Further, in a case where the entire inside surfaces of the flanges are flat, the area of the flanges contacting the tape edges becomes large and the tape edges are apt to be damaged. With the whole inside surface of the respective tape reel flanges being flat without radial ribs, when the recording tape is taken up by the tape reel at a high speed, air which once occupies a space between the bottom edge of the roll of the recording tape and the flange acts to raise a part of the recording tape layers to deteriorate tight winding of the roll of the recording tape, providing irregular winding of the recording tape. Tight winding of the tape is also effected by air enclosed between the laminated wound tape layers.